Referenceless Doppler Shift and Rate Estimation for Opportunistic Positioning With OneWeb Signals

We propose a technique for extracting the Doppler shift and its rate from OneWeb's Ku-band user downlink signals and demonstrate its suitability for opportunistic positioning. Since the downlink waveform and synchronization sequences are not publicly documented, the method exploits the periodicity inherent in the transmitted frames. By performing cross-correlation in the time domain between two consecutive bursts over several frame periods, we obtain an approximate estimate of the Doppler shift and a better accuracy estimate of the Doppler rate, even when the signal is received using a universal (low noise bloc) LNB without a parabolic reflector. The two estimates are merged in a Kalman filter, resulting in an unambiguous Doppler measurement that can be used in positioning calculations. Field experiments show that, for satellites above 67° elevation, the Doppler rate can be estimated with 13.25 Hz s⁻¹ (0.359 m s⁻²) precision and the Doppler shift with a standard deviation of 86.3 Hz (2.34 m s⁻¹). Frequency tracking is feasible down to 55° elevation, and simultaneous processing of three operational OneWeb frequency channels provides continuous measurement availability, with up to 50 % overlap between adjacent beams that further improves Doppler shift accuracy. Positioning using derived Doppler data resulted in a horizontal error of 384 m based on diffuse orbital data, which can be reduced using accurate satellite orbit and clock models. The algorithm is relatively simple and robust in low signal-to-noise ratio conditions, making it suitable for opportunistic use of OneWeb signals for positioning.